The furthest north I've been on 155 is the Chief Joseph longhouse, not quite to Nespelem, about a couple of miles north of where the Ponderosa pines begin these days. Further south still is where the road meets the river, heading upstream to Grand Coulee Dam, behind which Lake Roosevelt stretches forever. 155 clings to the slopes above the river, which hides in fog sometimes and glints in the sun othertimes.
Though the landscape looks like the dry West, water spills in from the flats above, seeps from the cliffs, and bubbles up from below. Steamboat Rock, which looks like it should be in a southwestern desert, is nearly surrounded by water. Sometimes gulls fly over, laughing in disbelief at their good fortune in the dry interior. Higher up, google mappers and other snoopers ogle the earth's surface. Search 'steamboat rock state park wa' in google maps, and in sat view you see a rainbow sunburst north of the rock, at least until they update the imagery. A proper blogger would link to this view, but I won't. I'm a blatherer, and have no time for such shepherding.
Now technically, 155 stops at the south end of Banks Lake, where the east walls of the canyon fall back and stretch into a plain, miles of settlement basin off to the side of the big floods, but a flood like Missoula cannot be dissipated so easily. the modern roadmap replicates what happened when the straight shot now filled by Banks passed this basin: 155 jags into 2 west for a couple miles, then drops into a long southward arc on what we call 17, but like 155 is just the Grand Coulee passage. After Dry Falls, a chain of lakes descends, but since the Columbia descends elsewhere and this part of the Coulee is un-damned, no river roars. The southernmost water before Grand Coulee spilt itself into a plain capacious enough to tame it is called Soap Lake, where suds scud across the wind-sept surface.
And here the coulee road becomes something else, a series of straight lines traversing squares enclosing irrigation circles. No teasing talus skirts, no chartreuse basalt columns, no flood-ripped canyon walls. Sure, it's better to follow 17 on down toward Moses Lake, more or less on the main flood channel, especially given the piss stench west of the fields west of Ephrata on Route 28. But avoiding urea-stink isn't quite the same thing as racing down the coulee, heading down the 155.